The only thing I'm aware of for changing resolution in safemode is from 800x600 to 600x400 or the other way. This is due to the display driver. without a driver that runs the advanced features of the display adapter windows won't beable to do much.
I know you can change the resolution to one of the above to corect a missconfigured setting, but that is all I have ever seen.
As to the setting being in the registry, that maybe true, but the display system will not redraw that to any other resolution other than 800x600 or 600x400, without a reboot, since you don't have dynamic updates with safemode...
Good luck